It may be better to use python2 explicitly

[astrojhgu]

On some systems, which has both python2 and python3, some meqtrees python scripts cannot run sucessfully. The reason is that these scripts are written in python2, while the first lines are "#!/usr/bin/python" or "#!/usr/bin/env python", which will point to python3.

[gijzelaerr]

is this on a ubuntu 16.04 system?

probably #!/usr/bin/env python2 is best then.

[astrojhgu]

Actually, my system is Archlinux, on which ls -lh /usr/bin/python /usr/bin/python -> python3

Also there is another compatible problem on my system. The python part of meqtrees need both pyfits and astropy, which are conflict on this system. If astropy is installed, pyfits can be obtained as

from astropy.io import fits as pyfits